This application requests continuing support for our studies of hapten-specific cloned human T cell lines (TCL). Specific objectives are proposed to correlate T cell function with the biochemical and genetic concomitants of recognition, to evaluate the role of the HLA complex in these processes and to characterize soluble regulatory products of hapten-specific TCL. We will investigate determinant recognition by hapten-specific HLA-DR, -DQ and -DP restricted TCL, employing recognition on allogeneic cell panels, blocking by monoclonal antibodies, and presentation by HLA-deletions. HLA-D region gene products will be compared to define new functional determinants and structural polymorphisms. Biochemical and molecular genetic techniques will be utilized to investigate differential expression of HLA class II molecules on resting versus activated or transformed subpopulations of Ia positive cells, and expression will be correlated with differences in antigen-presenting cell (APC) function. Alternative molecular contexts for recognition of haptenic determinants will be defined and related to requirements for processing by APC, employing both metabolically altered APC and artificial antigen-presenting matrices. We will also characterize a novel 50 kD cell surface glycoprotein expressed by some DR1+ lymphocytes that exhibits antigenic homology with alpha chains of HLA-DR molecules; employing somatic cell hybrids or artificial constructs between DR1+ APC with stimulatory versus nonstimulatory function, we will probe mechanisms for defective recognition on cells expressing the molecule. Finally, we will extend our studies of the functional activity of hapten-specific TCL by molecular characterization of an approximately 8 kD polypeptide hormone that has the capacity to stimulate proliferation of T8 positive lymphocytes with suppressor cell function. Biochemical and physical approaches to assessment of primary polypeptide structure will be combined with molecular genetic technologies for production and characterization of a cDNA probe encoding this molecule. Together the proposed studies will lead to clearer definition of the HLA restricting repertoire for hapten recognition and will provide new insights into cellular and molecular processes involved in regulation of human T cell responses.